1. Field of Invention
This invention generally relates to optical instruments, specifically to such instruments which are used for splitting optical spectrum.
2. Prior Art
Rainbow after raining often shows astonishing beauty in sky. The beautiful colors come from the broad band sunlight. When the individual components of the broad band spectrum of sunlight are separated through the refraction of the water drops in wetting air, a spectacular arch forms in sky. As in nature, in scientific fields, it is often necessary to split broad band optical spectrums and separate their individual components. The instruments used to separate or analyze light according to wavelength are known as spectroscopic instruments or spectrometers. The overall form of most current spectrometers is of an imaging system which consists of 3 principle components[1], collimating unit made of collimating lens, spectral unit, and camera or telescope unit made of focusing lens. The collimating unit collimates the input light into parallel beam light, the spectral unit separates the beam light and the camera or telescope unit output the separated components. In terms of image systems, by locating the spectral unit in the aperture stop of the system, the arrangement of the system is able to form a chromatically altered image of the entrance aperture or field stop. The field of view is defined by a field stop in the front focal plane of the collimating lens. The focusing lens completes the imaging of the field stop.
The spectral unit is the fundamental component of all spectrometers. In and near the visible region of the spectrum, this unit is usually a prism, a grating, a Fabry-Perot etalon, or a version of the Michelson interferometer[1]. These spectral units operate on plane waves. Prisms change the directions of these waves according to wavelength; gratings multiply and disperse them; etalons and Michelson interferometers change the irradiance of the waves according to their angle and wavelength. The collimating optics creates plane wave from the light emanating from each point in the entrance aperture. The focusing lens brings each plane wave leaving the spectral unit to a different point and makes the output ultimately analyzed spatially.
Therefore, all the spectrometers heretofore known suffer from a number of disadvantages:
(a) The overall form of most of the current spectrometers is a imaging system, it can only process beam light and plane waves, there is nothing to do with diffusion light and other type waves.
(b) In the current spectrometers, the beam light propagates in free space, therefore it can not be guided and distributed desirably.
(c) The resolving power of the current spectrometers is limited by the spectral separation mechanism.
(d) Single spectrometer can not cover broad range of spectrum in the mean time.
(e) The power throughput is limited by the intuitive nature of the current spectrometers, they are not appropriate to be used as power process equipment.
(f) The structure of the current spectrometers is complicate.
(g) The whole system of the current spectrometers is not compact.
(h) The structure of the current spectrometers is precise, so the whole system is not robust.
(i) The current spectrometers are usually used as independent spectral analyzing instrument, it is not easy to be integrated into other systems.
(j) The spectrometers in present use consisting of precise optics are very expensive.
As can be seen, the intuitive nature of the currently existing spectrometers limit their application to processing beam light and plane waves, there is nothing to do with diffusion light and other type of waves. The collimation optics and output optics are usually necessary for spectrometers to carry out spectrum separation function, this makes the structure of these systems too complicate. The input beam and output of the spectrometers all propagate in free space without guidance, therefore it is not easy to realize energy separation and collection of elements of broad band optical spectrum. The current spectrometers are more eligible to analyze spectrum. From the point view of energy application, the mechanisms of the currently existing spectrometers are not efficient in separation and collection of elements of broad band optical spectrum. The currently existing spectrometers depend on the aids of input optics and output optics to realize effective separation of broad band spectrum, the systems perform very well in spectral analysis and information process. However, they are not effective in carrying out spectral energy separation of broad band spectrum. Due to the complicate structure of spectrometers, they are not compact. In terms of power transportation, the currently existing spectrometers are not effective.